1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus.
2. Description of the Related Art
As an image forming apparatus using an electrophotographic system, such an apparatus has been conventionally known that steps including charging, exposing, developing, transferring and cleaning are sequentially carried out by using an electrophotographic photoreceptor (hereinafter, sometimes simply referred to as a “photoreceptor”). In the field of the image forming apparatus, improvements in image quality and service life of the apparatus are increasingly demanded in recent years, and improvements of the parts and systems are being investigated to deal with the demands.
For example, a photoreceptor used for writing an image is liable to receive stress upon charging and cleaning, and flaws and abrasion occurring on the surface of the photoreceptor bring about image defects. Members in contact with the photoreceptor (such as a charging roller and a cleaning blade) also receive stress, and it is necessary to prevent these members from being broken.
Accordingly, there has been proposed a method of preventing the surface of the photoreceptor from being damaged and preventing a member in contact with the photoreceptor from being broken by defining the dynamic hardness of the outermost layer of the photosensitive layer to a range of from 13.0×109 to 100.0×109 N/m2 (for example, in JP-A-2002-318459).
A system of transferring an image by using an intermediate transfer material is being frequently employed in recent years since the degree of freedom in paper to which the image is transferred. In an image forming apparatus equipped with an intermediate transfer material, however, foreign matters generated in the apparatus or getting into the apparatus intervene between the intermediate transfer material and the photoreceptor in some cases, whereby the photoreceptor is damaged, or the foreign matter sticking into the photoreceptor reach the electroconductive support. The problem is liable to occur particularly in the case where the intermediate transfer material has relatively high hardness in comparison to the electrophotographic photoreceptor. The problem causes photoreceptor leakage (which is such a phenomenon that an overcurrent locally flows in the photoreceptor), which brings about deficiency in image quality, such as colored spots on the formed image.
In recent years, furthermore, as a charging device of an electrophotographic apparatus, a charging device of a contact charging system, such as a charging roll, is being used instead of a non-contact charging device, such as a corona discharge device. A contact charging device has advantages in low ozone generation and low electric power consumption, but a higher voltage is applied to a photoreceptor by using a contact charging device than by using a non-contact charging device, whereby leakage is liable to occur in the photoreceptor suffering the aforementioned problems.
The amount of foreign matters generated in the apparatus (for example, generated from the developer and intermediate transfer medium having been deteriorated) or getting into the apparatus is increased associated with the use of an image forming apparatus for a long period of time, and therefore, it is important that the leakage is prevented from occurring for attaining at a higher level a long service life of the apparatus and high image quality.
One of the aims of the method disclosed in JP-A-2002-318459 is to prevent flaws of a photoreceptor from being formed, but it has been found as a result of investigations by the inventors that the method of JP-A-2002-318459 is insufficient for preventing leakage from occurring, and the photoreceptor disclosed in JP-A-2002-318459 is still has room for improvement in prevention of leakage.